The present invention pertains to a device for applying individual reinforcing threads onto a tubular layer made of polymer material that is additionally processed into a thread-reinforced unfinished tube made of polymer material consisting of several layers. The invention also pertains to a process for manufacturing a thread-reinforced unfinished tube made of polymer material that consists of several layers with the aid of such a device.
Tubes and diaphragm for air springs are typical products manufactured from a thread-reinforced polymer material. For example, the diaphragm of an air spring is subjected to high pressure. Such a diaphragm contains multiple reinforcing threads that are positioned close to one another with an equidistant spacing in order to withstand this pressure (a conventional diaphragm for an air spring contains, for example, approximately 200-300 reinforcing threads per 10 cm).
It has been known for a long time to manufacture a diaphragm for an air spring from individual plane layers, in which the reinforcing threads are already embedded. The individual layers are wound onto a mandrel and connected to one another within an overlapping region or a joint region, and then vulcanized. The diaphragm for the air spring is finished after this vulcanization.
The aforementioned process has the advantage that a large number of reinforcing threads spaced equidistant from each other can be easily embedded in a plane layer. However, it has been determined that the overlapping region or the joint region of the diaphragm may disadvantageously influence the physical properties of the diaphragm and also reduce the stability of the diaphragm within this region.
Therefore, it has already been proposed to manufacture a diaphragm for an air spring from an endless tube, into which the equidistant reinforcing threads are already incorporated. The advantage of this manufacturing process can be seen in the fact that the tube, from which the diaphragm is cut at the desired length, contains neither an overlapping region nor a joint region. However, it is relatively difficult to embed a large quantity of equidistant reinforcing threads into a tube. Different processes for realizing this feature have already been proposed.
One example of a coextrusion device for manufacturing a thread-reinforced unfinished tube made of polymer material is known from EP 0 605 767 A1. The unfinished tube consists of three layers, with two helically wound layers of equidistant reinforcing threads located between the first layer and the third layer. The two reinforcing thread layers are separated from one another by the second layer. The coextrusion device for manufacturing such an unfinished tube contains a first flow channel with circular cross section, which is concentrically surrounded by a second and a third flow channel with circular cross section. These flow channels are used to manufacture the individual polymer layers of the unfinished tube. A guide element for the first layer of reinforcing threads, which also has a circular cross section, is situated between the first and the second flow channel. One additional guide element for the second layer of reinforcing threads is situated between the second and the third flow channel. The guide elements for the reinforcing threads are arranged in a rotating fashion between the flow channels so as to make it possible to embed the reinforcing threads in a helical pattern between the individual layers of the unfinished tube. Each guide element contains a series of equidistant guide channels, with one reinforcing thread being guided in each guide channel. The flow channels and the guide elements have the shape of a cone and taper in the longitudinal direction to the diameter of the unfinished tube to be manufactured.
An unfinished tube that contains two layers of helically wound, equidistant reinforcing threads can be manufactured in one step with the coextrusion device known from EP 0 605 767 A1. However, a complicated preparation of the coextrusion device is required before the manufacture of the unfinished tube can begin because the reinforcing threads must be individually guided through the guide channels of the guide elements.
U.S. Pat. No. 4,578,024 pertains to a coextrusion device that has a design similar to the coextrusion device known from EP 0 605 767 A1. This device also makes it possible to manufacture an unfinished tube with equidistant reinforcing threads in one step. In this coextrusion device, each individual reinforcing thread is guided into an assigned guide channel, so that a complicated preparation of the coextrusion device is also required in this case before the manufacture of the unfinished tube can begin.
Accordingly, it is an object of the present invention to enable the applying of individual reinforcing threads onto a tubular layer made of polymer material to provide a simple manufacture of an unfinished tube with equidistant reinforcing threads and can be easily prepared for the manufacturing process.
Another object of the invention is to enable simple preparation and execution for the manufacturing of a thread-reinforced unfinished tube made of polymer material.
The above and other objects of the present invention can be achieved by a device for applying individual reinforcing threads onto a tubular layer of polymer material that can then be processed into a thread-reinforced unfinished tube of polymer material comprising a plurality of layers.
The device contains a positioning ring with at least one row of equidistant holes on a circumferential line, wherein the reinforcing threads are guided from radially outward to radially inward through the aforementioned holes at an inlet angle relative to the longitudinal axis of the positioning ring.
Further, the device contains a rotationally symmetric, funnel-shaped deflection element that surrounds one continuously tapering channel with an annular inlet surface and a smaller annular outlet surface, wherein the reinforcing threads are guided on the rotationally symmetric radially inner surface of said deflection element.
At the inlet surface, the deflection element has an inlet angle xcex1 relative to the longitudinal axis of the deflection element, which corresponds to a great extent to the inlet angle of the reinforcing threads relative to the longitudinal axis of the positioning ring.
At the outlet surface, the deflection element has an outlet angle xcex2 relative to the longitudinal axis of the deflection element that lies between approximately 0xc2x0 and 25xc2x0, preferably between 0xc2x0 and 10xc2x0.
The deflection element is concentric with and surrounded by the positioning ring and axially aligned relative to the positioning ring in such a way that reinforcing threads that are radially guided through the holes of the positioning ring can be directly guided into the inlet surface of the deflection element.
It is a feature of the invention to achieve the above and other objects by a process wherein:
a reinforcing thread is guided from radially outward to radially inward through each hole of the positioning ring at an inlet angle relative to the longitudinal axis of the positioning ring, and
the reinforcing threads are placed onto the radially inner surface of the deflection element and deflected by the inlet angle into a largely axial direction by the deflection element, with the reinforcing threads under constant tension, and with the following steps being carried out in order to manufacture a thread-reinforced unfinished tube:
a first layer of polymer material is applied onto a rotationally symmetric mandrel in a first processing station,
the mandrel coated with the first layer is concentrically guided from the inlet surface of the deflection element through the outlet surface of the deflection element such that the reinforcing threads situated on the radially inner surface of the deflection element are deposited on the radially outer surface of the first layer with an equidistant spacing from one another, and
the mandrel coated with the first layer is transferred to at least one additional processing station, in which another layer of polymer material is applied to the first layer.